[media] em28xx: drop last soc_camera link

The em28xx driver still used the soc_camera.h header for the ov2640
driver. Since this driver no longer uses soc_camera, that include can
be removed.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>